Divacancy in 3C- and 4H-SiC : An extremely stable defect

Abstract

Using first-principles calculations for divacancy defects in 3C− and 4H−SiC, we determine their formation energies and stability, their ionization levels, and relaxed geometries (symmetry point groups) for neutral as well as for charged states. For 4H−SiC all four possible nearest-neighbor divacancy configurations are considered. We find not only a remarkable high binding energy of about 4 eV, but also a strong site dependence (cubic or hexagonal lattice sites) of the formation energies. Applying a Madelung-type correction to deal with the electrostatic interactions between charged supercells, our results indicate a negative-U behavior at EV+0.7 eV between the charge states 1+/1− only for nearest-neighbor divacancies on different lattice sites (mixed cubic and hexagonal) in 4H−SiC, but not for all the other cases (pure cubic or pure hexagonal) in 4H− or for the cubic divacancy in 3C−SiC.